A Map of Content (MoC) is a note containing links to other notes. It’s a meta note. It can be thought of as an index of notes on a specific topic, question, perspective, or area of interest. Just like a table of contents.
While each note can only be stored in a single folder on your computer, many MoCs can link to the same note. This is a much more powerful paradigm. In that sense, MoCs are “folders” on steroids (like tags!).
Here’s an analogy. If links and backlinks are like roads, tags are like road signs, folders are like houses and MoCs are maps. It’s not that one is better than the other: they’re complementary.
In my knowledge base, I have MoCs about note-taking, PKM, psychology, motivation, productivity, etc. Each of those MoCs contains many links to related notes. Through those MoCs, I can connect ideas from neuroscience with notes about productivity or PKM.
This is the most basic form of Map of Content: a simple list of links. Actually, MoCs can be more useful and powerful. While tags “only” link different notes together, MoCs can add context to links, making those more meaningful and more valuable. It is often mentioned that knowledge can be represented as a graph. And within graphs, nodes matter, but the connections between nodes matter just as much.
When you get started, you probably won’t need those right away. But as your knowledge base grows, MoCs will become more and more appealing.
MoCs help locate content across the whole knowledge base, independently of where the notes are stored (folders) and independently of their tags. MoCs help aggregate and connect ideas pulled from various places. They also help keep your knowledge base manageable as it scales. Finally, MoCs add one more way to navigate across your notes, which strengthens navigability in your PKM.
You can even go further and create a "MoC of MoCs” to list all your MoCs and add information about the relationships between your MoCs.
These add one more metadata layer to your knowledge graph, allowing you to express ideas at the intersection of multiple topics.